Electrophotographic optical printers using a laser light source have been in use for some time. Recently, the use of optical printers, which have an LED array as the light source, have gained considerable popularity. These printers require an LED device for modulating light emitted by the LED array to form an Heretofore, this end has been attained by combining the LED with a self-focussing lens, an optical fiber array, or a similar optical waveguide.
Unfortunately, these prior art arrangements suffer from certain inherent limitations caused by optical coupling which leads to a high degree of optical attenuation and an unsatisfactory output efficiency. Efforts to enhance optical input include the use of an optical chemical-vapor deposition (CVD) or photo polymerization process, each of which permits formation of lenses directly on LEDs. However, in order to fabricate a material that will constitute the lens at a designated position, it is necessary to expose that position to focussed light. In view of the fact that a typical light emitting diode array comprises several thousand elements, lenses prepared in this manner must be formed in many regions. This type of process is extremely time-consuming and inefficient.
Recently, efforts to overcome this difficulty have focused upon the preparation of an LED array head which forms a light source for exposure that may be used to simultaneously expose several thousand locations. However, such efforts have not been successful due to the fact that in those cases in which the exposure pitch varies from product to product, or lot to lot, the technique is not applicable.